A variety of systems implement master and slave (or master/slave) valves to control, for example, pressure in a chamber. In such systems the slave valves follow the lead of the master valve. As such, the slave valves are intended to be responsive to movement of the master valve. It is often a goal of such systems that the master and slave valves operate in concert, and as close to simultaneously as possible.
The difference in time between the movement of the master valve and the movement of the slave vales is referred to as the response time. To achieve near simultaneous operation between the master and slave valves, response time should be minimized. Because communication between the master valve and slave valves occurs via a communication path and the slave valves need to each process and respond to a master valve position signal (sometimes referred to as the setpoint), certain challenges to minimizing response times exist.
In a typical valve system, the position of the master valve has been embodied in an analog signal (e.g., 0-10 Volts) communicated to the slave valves via a copper path. An analog communication method is fast, but it is susceptible to noise. To achieve accuracy noise should be removed, if not eliminated. In reality, it is difficult to achieve high resolution without utilizing heavy low-pass filters to reduce the noise. Use of low-pass filters can, however, increase the response time. Also, since the analog pressure setpoint is converted into a digital signal by an analog-to-digital (“A/D”) converter at the slave valve, digitizing the noise (i.e., the least significant bit (LSB) of the word) can create an undesired jittering of the position of the slave valves.
In an analog implementation, even 1 LSB jitter in the gate or flapper position of a slave valve can produce significant mechanical vibration that is undesired in many pressure control applications. A pressure transducer is typically used to provide pressure feedback to a pressure controller that is used for controlling the valves. Mechanical feedback can occur, where the pressure transducer that provides the pressure feedback signal responds to the mechanical vibrations. The pressure controller will respond to this signal from the pressure transducer, which will lead to pressure control instability. When there are many slave devices, this unwanted mechanical motion will be more pronounced, which is more likely to cause unwanted pressure control disturbances. Thus, achieving accurate and stable valve control in a highly responsive system provides myriad interrelated challenges.